Varnish Installation Guide

This document explains how to install Varnish Reverse Proxy for LibreNMS.

Varnish is caching software that sits logically between an HTTP client and an HTTP server. Varnish caches HTTP responses from the HTTP server. If an HTTP request can not be responded to by the Varnish cache it directs the request to the HTTP Server. This type of HTTP caching is called a reverse proxy server. Caching your HTTP server can decrease page load times significantly.

Simplified block diagram of an Apache HTTP server with Varnish 4.0 Reverse Proxy.

Block Diagram 1

CentOS 7 Varnish Installation

In this example we will assume your Apache 2.4.X HTTP server is working and configured to process HTTP requests on port 80. If not, please see Installing LibreNMS

Install Varnish 4.0 RPM

  • Enable the Varnish CentOS 7 repo and install
rpm --nosignature -i
yum install varnish

By default Varnish listens for HTTP requests on port 6081.

  • Temporarily add a firewalld rule for testing Varnish.
firewall-cmd --zone=public --add-port=6081/tcp

Test Varnish

  • Start Varnish
systemctl start varnish

Using a web browser navigate to :6081 or You should see a Varnish error message, this shows that Varnish is working. Example error message:

Error 503 Backend fetch failed

Backend fetch failed

Guru Meditation:

XID: 3

Varnish cache server

Edit Varnish Parameters

Now we need to configure Varnish to listen to HTTP requests on port 80 and relay those requests to the Apache HTTP server on port 8080 (see block diagram).

  • Stop Varnish.
systemctl stop varnish
  • Create a back-up of varnish.params just in case you make a mistake.
cp /etc/varnish/varnish.params /etc/varnish/varnish.params.bak
  • Edit the varnish.params config.
vim /etc/varnish/varnish.params

Set the VCL location, IP address, port, and cache location and size. malloc sets the cache location to RAM, and 512M sets the cache size to 512MB.


Example varnish.params:

# Set this to 1 to make systemd reload try to switch vcl without restart.

# Main configuration file. You probably want to change it.

# Default address and port to bind to. Blank address means all IPv4
# and IPv6 interfaces, otherwise specify a host name, an IPv4 dotted
# quad, or an IPv6 address in brackets.

# Admin interface listen address and port

# Shared secret file for admin interface

# Backend storage specification, see Storage Types in the varnishd(5)
# man page for details.

# Default TTL used when the backend does not specify one

# User and group for the varnishd worker processes

# Other options, see the man page varnishd(1)
DAEMON_OPTS="-p thread_pool_min=5 -p thread_pool_max=500 -p thread_pool_timeout=300"

Configure Apache for Varnish

Edit librenms.conf and modify the Apache Virtual Host listening port.

  • Modify:<VirtualHost *:80> to: <VirtualHost *:8080>
vim /etc/httpd/conf.d/librenms.conf

Varnish can not share a port with Apache. Change the Apache listening port to 8080.

  • Modify:Listen 80 to:Listen 8080
vim /etc/httpd/conf/httpd.conf
  • Create the librenms.vcl
cd /etc/varnish
touch librenms.vcl
  • Set ownership and permissions for Varnish files.
chown varnish:varnish default.vcl varnish.params secret
chmod 644 default.vcl varnish.params secret

Edit the librenms.vcl.

vim librenms.vcl

Paste example VCL config, read config comments for more information.

# This is an example VCL file for Varnish.
# It does not do anything by default, delegating control to the
# builtin VCL. The builtin VCL is called when there is no explicit
# return statement.
# See the VCL chapters in the Users Guide at
# and for more examples.

# Marker to tell the VCL compiler that this VCL has been adapted to the
# new 4.0 format.
vcl 4.0;

# Default backend definition. Set this to point to your Apache server.
backend librenms {
    .host = "";
    .port = "8080";

# In this example our objective is to cache static content with Varnish and temporarily
# cache dynamic content in the client web browser.

sub vcl_recv {
    # HTTP requests from client web browser.
    # Here we remove any cookie HTTP requests for the '' host
    # containing the matching file extensions. We don't have to match by host if you
    # only have LibreNMS running on Apache.
    # If the cookies are not removed from the HTTP request then Varnish will not cache
    # the files. 'else' function is set to 'pass', or don't cache anything that doesn't
    # match.

    if ( ~ "^") {
        set req.backend_hint = librenms;
        if (req.url ~ "\.(png|gif|jpg|jpeg|ico|pdf|js|css|svg|eot|otf|woff|woff2|ttf)$") {
            unset req.http.Cookie;


sub vcl_backend_response {
    # 'sub vcl_backend_response' is the same function as 'sub vcl_fetch' in Varnish 3, however,
    # the syntax is slightly different
    # This function happens after we read the response headers from the backend (Apache).
    # First function 'if (bereq.url ~ "\' removes cookies from the Apache HTTP responses
    # that match the file extensions that are between the quotes, and cache the files for 24 hours.
    # This assumes you update LibreNMS once a day, otherwise restart Varnish to clear cache.
    # Second function 'if (bereq.url ~ "^/' removes the Pragma no-cache statements and sets the age
    # of how long the client browser will cache the matching urls.
    # LibreNMS graphs are updated every 300 seconds, 'max-age=300' is set to match this behavior.
    # We could cache these URLs in Varnish but it would add to the complexity of the config.

    if ( ~ "^") {
        if (bereq.url ~ "\.(png|gif|jpg|jpeg|ico|pdf|js|css|svg|eot|otf|woff|woff2|ttf)$") {
            unset beresp.http.Set-cookie;
            set beresp.ttl = 24h;

        if (bereq.url ~ "^/graph.php" || "^/device/" || "^/iftype/" || "^/customers/" || "^/health/" || "^/apps/" || "^/(plugin)$" || "^/(alert)$" || "^/eventlog/" || "^/graphs/" || "^/ports/" ) {
            unset beresp.http.Pragma;
            set beresp.http.Cache-Control = "max-age=300";

sub vcl_deliver {
    # Happens when we have all the pieces we need, and are about to send the
    # response to the client.
    # You can do accounting or modifying the final object here.

    return (deliver);
  • Reload rules to remove the temporary port rule we added earlier.
firewall-cmd --reload

Varnish caching does not take effect immediately. You will need to browse the LibreNMS website to build up the cache.

Use the command varnishstat to monitor Varnish caching. Over time you should see 'MAIN.cache_hit' and 'MAIN.client_req' increase. With the above VCL the hit to request ratio is approximately 84%.

  • Session based VCL (coming soon)

  • Testing and debugging VCL (coming soon)